1. Field of the Invention
The present invention relates to a dual-side use disk player of the type in which data is played back from both sides of a data record disk (referred to as a disk) consisting of a pair of circular substrates each having a signal recording layer.
2. Prior Art Description
There has been known a dual-side use disk player. In this type of disk player, a disk consists of a pair of circular substrates each having a recording layer. A pair of pick-ups is provided for the recording layers on both sides of the disk. With provision of the pair of pick-ups, data can be played back from the recording layers on both sides of the disk, without flipping over the disk. With such a structure, in the case where the circular substrates, which are bonded together to constitute the disk, are radially displaced by a distance "e" from each other, (see FIG. 1). the circular substrates must be individually centered on a turntable, to ensure a smooth playback of data from the recording layers on both sides of the disk.
FIG. 1 is a sectional view showing a disk clamp mechanism constituting a key portion of a conventional dual-side use disk player in which the disk substrates are individually centered on the turntable for playing back the recorded data, and a disk centering means for centering the disk on the turntable.
As shown in FIG. 1, a turntable 2 is fixed to and turns with a spindle shaft 1 of a spindle motor. A disk 3, which is to be placed on the turntable 2, consists of a pair of circular substrates 3a and 3b bonded together, which respectively have signal recording layers. A disk support surface 2a of the turntable 2 has a recessed area. A first centering member 5, which is provided within the recessed area, is arranged such that it moves up and down with respect to the disk support surface 2a. The first centering member 5 is guided by the shaft 1, biased by a coiled spring 6, and centers the circular substrate 3b of the disk 3 through a center hole of the circular substrate 3b.
A support member 7 is provided above the turntable 2, and is movable in a direction orthogonal to the disk support surface 2a of the turntable 2. Further, a means (not shown) is provided to position the support member 7 at three positions, a non-clamping position as shown in FIG. 1, and first and second clamping positions as shown in FIGS. 2 and 3.
A pushing means including a rotating member 8 and a disk contact member 9, which is rotatably and vertically, movably provided on the support member 7, pushes the disk 3 toward the turntable 2. More specifically, the rotating member 8 contains a column part 8a and a flange 8b. The column part 8a of the rotating member 8 is movably inserted in an opening 7a of the support member 7. The rotating member 8 is in contact with an inner race 10a of a ball bearing 10. An intermediate member 10c is fixed to an outer race 10b of the ball bearing 10. The member 10c, when operated, contacts a stopper 11, which is made of resilient material and is mounted on the lower surface of the support member 7.
The disk contact member 9, which cooperates with the rotating member 8 to form the pushing means and comes in contact with the disk 3, is movable in the axial direction of the rotating member 8. A coiled spring 12 is placed between the rotating member 8 and the disk contact member 9.
A second centering member 13, mounted to the rotating member 8, is movable in the axial direction of the rotating member 8. The second centering member 13 is for centering the circular substrate 3a of the disk 3 through a center hole of the substrate 3a. The second centering member 13 is supported by a lug 8d of the rotating member 8. A coiled spring 14 is placed between the rotating member 8 and the second centering member 13.
A pair of optical pick-ups 16 and 17 are provided between which the disk 3 is placed on the turntable 2. The pair of pick-ups are guided and moved along the recording surfaces of the disk 3 by means of a drive means (not shown).
Operations of the dual-side use disk player thus arranged will now be briefly described. A first operation of the player is to play back data stored in a recording layer of the circular substrate 3b of the disk 3, i.e., the substrate in contact with the turntable 2. During operation, the support member 7 is moved from the non-clamping position shown in FIG. 1 toward the turntable 2, and is positioned at the first clamping position shown in FIG. 2. At this position, the disk contact member 9 comes in contact with the disk 3, and the coiled spring 12 is compressed. The compressed spring pushes the disk 3 against the turntable 2. At the same time, the first centering member 5 is urged into the center hole of the circular substrate 3b. to center the substrate 3b on the turntable. At this time, the flange 8b of the rotating member 8 moves away from the support member 7. The intermediate member 10c, fixed to the outer race 10b of the ball bearing 10, comes in contact with the stopper 11 of the lower surface of the support member 7, with a predetermined resistance existing therebetween. Under this condition, the turntable 2 is rotated, while the lower side optical pick-up 17 picks up data from the recording layer on the substrate 3b.
Now, an operation to play back data of the recording layer on the circular substrate 3a of the disk will be described. In the operation, the support member 77 is further moved toward the turntable 2 and reaches the second position shown in FIG. 3. Accordingly, the rotating member 8 descends on the disk contact member 9 that has been in contact with the disk 3 and in a fixed state. The coiled spring 14 is then compressed and urges the second centering member 13, that has been supported by the lug 8d of the rotating member 8, to enter the center hole of the circular disk 3a, so that the disk 3 is slightly displaced in the radial direction. At the same time, a tubular portion of the second centering member 13 comes in contact with the first centering member 5, to push the first centering member 5 out of the center hole of the circular substrate 3b and to set it below the level of the disk support surface of the turntable 2. Through the above operation, the circular substrate 3a is centered on the turntable 2. Under this condition, the turntable 2 is reversely rotated, while the optical pick-up 16 disposed above the disk 3 picks up data recorded in the recording layer on the circular substrate 3a.
In the disk player thus arranged, when data is played back from the recording layer on the upper circular substrate 3a, which is not yet in contact with the turntable 2, the coiled spring 12, which has been compressed to bias the disk contact member 9 by a certain force, is further compressed. In a situation where the pressure on the disk is extremely high, and a coefficient of friction between the disk 3 and the disk support surface of the turntable 2 is increased due to humidity, for example, the frictional force is greatly increased between the disk and disk support surface. Under this condition, if the second centering member 13 is inserted into the center hole of the substrate 31, the disk 3 will not move in a radial direction, resulting in failure of the centering of the disk on the turntable.
In a disk clamping mode, the support member 7 is constantly in contact with the ball bearing 10. Therefore, an external vibration having an adverse effect on the playback of the disk is transferred through the support member 7, the ball bearing 10 and the rotating member 8 to the second centering member 13 and the first centering member 5, and finally to the disk 3.
The ball bearing 10 must be of the radial type, and rotate at a high speed for a long time while being subjected to a large thrust load. At this time, the required rotating accuracy must be ensured. Use of a ball bearing of such a superior durability leads to an increased cost to manufacture.